Abstract: A number of geothermometers and geobarometers involving coexisting garnet, biotite, and cordierite have been used to calculate the pressures and temperatures of metamorphism of the Cashel thermal aureole in Connemara. Temperatures from the garnetbiotite thermometer show a wide variation between calibrations, and are markedly different from those obtained from the garnet-ordierite thermometer. These variations, together with the possibility of extensive reequilibration between garnet and cordierite rims and biotite, indicate that the use of exchange reaction thermometry, for these rocks at least, may be invalid. The various calibrations of the garnet-cordierite-sillimanitequartz geobarometer give reasonably consistent pressure estimates which, after allowance for partial pressures of water, indicate pressures of metamorphism of about 5±1 kb.